It has long been known that organo polysiloxanes may be incorporated into organic polymer compositions to modify the processing characteristics thereof. For example, it is known that extrudability and calendering of such materials may be improved by incorporating therein liquid dimethylpolysiloxanes. U.S. Pat. No. 3,691,257 describes the addition of polystyrene-polydimethylsiloxane-polystyrene triblock copolymers to organic polymers in order to beneficially modify the surface properties of organic polymers and compositions containing them.